Communication system



Sept. 18,1945. R. H. HERRICK COIIUHICATION SYSTEI Filed April 17, 1944 INVENTOR. ROSWELL H. HERRIQK H mzoikhm V mohoudum .2.

$15 .Ill 5 S2: 3

Arro' n EY Patented .Sept. 18, 1945 UNITED STATES PATENT OFFICE ooMMUNIoA'rIoN SYSTEM I Roswell H. Herrick, Oak Park, 111., assigno'r-to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application April 17, 1944, sesame. 531,381

11 Claims. ('01. 179--42)' This invention relates to improvements in a telephone system of the type using regular telephone substation sets and a central exchange and a separate intercommunicating system in which loudspeaking equipment is provided.

, The invention is herein illustrated and described as applied to an intercommunicating syst-ernin whicheach station is'provided with a transducer adapted to be used as a loudspeaker or as a microphone, a key which normally occupies a listen position but is operable to a displaced talk position, an amplifier for outgoing signalsand station selecting keys.

. ;When a loudspeaking intercommunicating station=is located in an area where the background noise at times may behigh, it is desirable to provide an auxiliary transmitter and receiver which can be used in place of the customary transducer to provide a higher signal to noise ratio for both incoming and'outgoing speech signals. Such an arrangement can also be used to provide greater privacy of the conversation in locations that are not necessarily noisy. 'IntercQmmuni eating systems are often used to provide rapid communication between executives of large business firms. In this case the transducerand control keys are usually installed on the executives desk. A separate telephone system having a cen tral automatic exchange or manual switchboard is usually provided for communication between the subordinates. Since the executives must also communicate with the subordinates a telephone set includingthe usual transmitter and receiver must-also be'providedon his desk 'for use with the central exchange substation. both practical and economical to use the transmitter and receiver of the regular telephone-Sula station set as auxiliary equipment for the inter-'' communicating system. Furthermore, by incorporating the telephone substation set in the intercommunicatin station unit a considerable saw ing in'desk space can be 'eflected.

The'pr'incipal object of the present invention A feature of the invention is the provision of means for reducing the sensitivity of the transmitter' and receiver of the substation set when they are used with the intercommunica'ting system to" a value consistent with the sensitivity of thetransducer which is normally used It is therefor Other features will appear upon, a further perusal of the specification and the accompanying drawing which discloses a single embodiment of the invention applied to an intercommunicating systemaspreviously described and a telephone substation set of the automatic anti-sidetone type in which the transmitter and-receiver are combined in a handset.

The transducer of each intercommunicating set isnormally connected to an interstation conductor that is multipled to a station selecting key at each of thecther stations; The output of any amplifier can be connected to the transducer-of any other station by operating a station selecting key and the talk key; Operation of the talk key also transfers the transducer from the interstation conductor to the amplifier input. The transducer is then used as a microphone, its output being amplified before it is applied to the transducer of another station for reproduction. When the talk key is in its normal position the transducer is "prepared for use as a loud-speaker to reproduce signals received from other stations. Conversation'is thus permitted in only one directionjat a time, the talk key beingused to switch from the talking to listening conditions. A switch is provided to transfer the transmitter and receiver-of thetelephonesubstation set that is connected'to thecentral exchange line tothe intercommunicating station unit. This prepares circuits for replacing the transducer and the talk key by the handset upon removal'of the handset from its cradle. When the handset is in use with the intercommunicating system the receiver of the handset is connected to the interstation conductor and thetransmitter is'connected to the amplifier'input. The use of. the talk key is then eliminated anda two way conversation can be conducted without any further key-operations by v the party using'the handset. i

The'operation' will nowbe described'in greater detail with reference to the drawing. The filaments of the am'plifie'r tubes are normally energized by the power supply but the plate supply circuit isopen." To originate a call the selector key 0: the desired station andthe talk key are operated. The transducer I is transferred from the'i'nt'erstation conductor 2 to the input of the amplifierby contacts 3 of the talk key. The output of the amplifier is connected to the'input or the called stationuirough contact 4 of the talk key and the operated selector key. The ampl'ifier pl'ate'supply is completed lay-contacts 5 of the talklizeyj Thecalling party speaks into his -wi to signal the calledparty and to identify himself. The voice currents created by the transducer are amplified before being reproduced by the transducer at the called station. The talk key is then restored to its normal listening position. The called party answers by operating his talk key and the selector key corresponding to the calling station. The transducer I at the calling station reproduces the output of the amplifier at the called station which is connected to the input conductor 2 by the talk key and the operated selector key at the called station.

When the transfer switch 6 is thrown to the right the transmitter I and receiver 8 of the handset 9 are connected to the telephone substation set as in a conventional automatic anti: sidetone telephone substation set so that calls may be extended therefrom over th central exchange line. The substation set differs from the conventional design only in the fact that the connections are completed through contacts of the transfer switch I5 and in the addition of conar Q e crad e sw ch r ho s it h- These addition contacts on the cradle switch have no connection with the central exchange but are employed only when the handset is used with the interconimunicating system. Transfer switch 6 also short-circuits condenser I I. If this was not done it would become charged to the full voltage of the amplifier plate supplyand would cause a heavy transient current to flow through the transmitter I if the transfer switch 6 was operated to the left while the handset 9 was off of the cradle. This might injure the transmitter and would also create a transient current in the amplifierwhich would be amplified and might produce an objectionable click in the transducer of a connected intercommunicating station.

When the transfer switch It i thrown to the left blade I2 transfers one terminal of the receiver 8 from the substation set to voltage divider I8, blade I3 transfers the common connection of transmitter I and receiver 8 from the substation set to ground, blade I4 transfers the other terminal of the transmitter I from the substation set to the voltage divider III in series with condenser 20 and also prepares a direct current circuit to the transmitter I in series with relays 2| and 22,

blade I5 disconnects one side of the central ex- 7 change line from the cradle Switch to prevent the connection of induction coil 23 and condenser 2 to'the central exchange line when the handset 9 is removed from the cradle switch. If this con- 7 nection was not opened by the transfer switch 6 the ringer 25 would be shunted by the induction coil 23 and condenser 24 which would prevent proper operation of the ringer if the substation is signalled from the central exchange while the handset is being used with the intercommunicating system. Blade I6 transfers condenser 26 from the cradle switch to the ringer 25 so that the substation can be signalled by the central exchange when the handset is being used with the intercommunicating set. Blade I I removes the previously described shunting circuit from condenser II.

With the transfer switch 6 thrown to the left the removal of the handset 9 from its cradle operatesthe cradle switch contacts III which remove a second shunting circuit from condenser II' and complete a direct current circuit from +B of the power supply through resistor 21, contacts Ill, relays 2| and 22, and the transmitter I to ground and-B of the power supply. Resistor 21 and relays 2I and 22 limit the current to the proper value for the transmitter I. This current also operates relays 2 I and 22.

close to the users mouth and ear.

The operation of relay 2I connects the amplifier input to voltage divider I9 through contacts 28 and completes the plate supply to the amplifier through contacts 29. The operation of relay 22 connects the output of the amplifier to the input of a connected station through contacts 30 and the operated selector key, and also transfers the interstation conductor 2 from the talk key to voltage divider I8 at contacts 3|.

Speaking into the transmitter I will cause its resistance to vary in accordance with the varying sound pressure which will cause an alternating current to flow through condenser 20 and voltage divider I9. This alternating current is prevented from flowing through the power supply by the filter consisting of relays 2I and 22 and condenser I I. A portion of the voltage produced across voltage divider I9 is applied to the input of the amplifier. Any alternating voltages superimposed on the plate supply voltage by the amplifier plate current variations are excluded from the input circuit by the filter formed by resistor 2! and condenser I I. The voice currents are amplified and then reproduced by the transducer at the connected station. Incoming signals are applied to voltage divider I8. A portion of the voltage developed across voltage divider IB is applied to receiver 8 for reproduction. If the connected station is similarly equipped with an auxiliary handset, a two way conversation may be conducted without any further key operations by either party. Voltage dividers I8 and I9 are provided because the transmitter I and receiver 8 of the handset are more sensitive than the transducer I, in addition they are held close to the mouth and ear of the user. The voltage dividers compensate for these differences. Although the transmitter I is sensitive and is used for close talking it does not have suificient output to operate the transducer at the connected station directly. For this reason the amplifier is also used with the handset transmitter I. The signal to noise ratio is increased when the handset is used because the transmitter I and receiver 8 are held Greater privacy of conversation is also secured since the user may then speak in a lower voice and the volume of the signals reproduced .by the receiver is too low to permit other persons in the vicinity from overhearing.

Although the invention has been disclosed in connection with the specific details of preferred embodiments thereof, it must be understood that such details are not intended to limit the invention except insofar as set forth in the appended claims.

Having thus described the invention, what is claimed as new and is desired to secure by Letters Patent is:

1. In a communication system, a station comprising amplifying means and a telephone substation set having a transmitter and a receiver, a line extending from said telephone substation set to a central exchange, a second station, an intercommunicating line for connecting said amplifying means to said second station, switching means at said first station for disconnecting the transmitter thereat from said telephone sub-,- station set and for associating it with said amplifying means, and means for reducing the output ofsaid transmitter when so associated.

2. In a communication system, a station comprising amplifying means and a telephone substation set having a transmitter and a receiver, a line extending from said telephone substation set to a central exchange, a second station hav ing sending and receiving circuits, an intercommunicating line for connecting said amplifying means to the receiving circuit of said second station, a second intercommunicating line for connecting the sending circuit of said second station to said first station, said intercommunicating lines establishing two independent one way communication channels between said stations when so connected, and switching means at said first station for disconnecting the transmitter and receiver thereat from said telephone substation set and for associating them with said amplifying means and with said second intercommunicating line respectively.

3. In a communication system, a station comprising a loud-speaker, amplifying means, and a telephone substation set having a transmitter, a receiver, and a hookswitch, a line extending from said telephone substation set to a central exchange, a second station, an intercommunicating line for connecting said amplifying means to said second station, a second intercommunicating line normally connected to said loudspeaker, switching means at said first station for disconnecting the transmitter and receiver thereat from said telephone substation set, and means controlled by said hookswitch for associating said transmitter and receiver with said amplifying means and with said second intercommunicating line respectively and for simultaneously disabling said loud-speaker.

4. In a communication system, a station comprising amplifying means and a telephone substation set having a transmitter, a receiver, and a hookswitch, a line extending from said telephone substation set to a central exchange, a second station, an intercommunicating line for connecting said amplifying means to said second station, a second intercommunicating line extending from said first station to said second station, switching means at said first station for disconnecting the transmitter and receiver thereat from said telephone substation set, and means controlled by said hookswitch for associating said transmitter and receiver with said amplifying means and with said second intercommunicating line respectively and for simultaneously conditioning said amplifying means for use.

5. In a communication system, a station comprising amplifying means and a telephone substation set having a transmitter, a receiver, and a hookswitch, a line extending from said telephone substation set to a central exchange, a source of current, switching means for disconnecting the transmitter from said telephone substation set and preparing a supply circuit to it from said source of current, and means controlled by said hookswitch for completing the supply circuit to said transmitter and for associating it with said amplifying means.

6. In an intercommunication system, a plurality of stations each having a transducer adapted to be used as a loudspeaker or as a microphone, and switch means for controlling communication between two of said stations, said switch means being so constructed and arranged that one-way communication in either direction can be carried on through alternate operation of said switch means at said two stations, amplifying means and a telephone handset having a transmitter and a receiver at one of said stations, and means controlled by said telephone handset for associating said transmitter with said amplifying means and for replacing said transducer with said receiver to permit two-Way communication without further operation of said switch means at said one station.

7. In an intercommunication system, a plurality of stations each having a transducer adapted to be used as a loudspeaker or as a microphone, and switch means for controlling communication between two of said stations, said switch means being so constructed and arranged that one-way communication in either direction can be carried on through alternate operation of said switch means at said two stations, amplifying means and a telephone handset having a transmitter and a receiver at one of said stations, and means for associating said transmitter with the amplifying means of said one station and for associating said receiver with the other of said stations.

8. In an intercommunicating system as claimed in claim 7, means at said one station for applying only a portion of the incoming signal voltage to said receiver when the handset is being used.

9. In an intercommunicating system as claimed in claim '7, means at said one station for applying only a portion of the signal voltage produced by said transmitter to said amplifying means.

10. In a telephone system, a substation having a transducer, amplifying means, and a conventional transmitter and receiver, an intercommunicating lin normally connected for use with said transducer and said amplifying means, an exchange line normally connected to the transmitter and receiver, switching means to disconnect said transmitter and receiver from said exchange line and to connect them for use with said amplifying means and said intercommunicating line, and means for reducing the output from the transmitter and the input to the receiver when used with the intercommunicating line.

11. In an intercommunicating system, a common battery exchange line, a local line, a substation having loud-speaking equipment connected for use with the local line and a transmitter and receiver connected for use with the exchange line, means for switching the transmitter and receiver for use with the local line, and means operated when a call is extended from the transmitter and receiver over said local line for supplying a local battery feed to the transmitter and reducing the output of the transmitter fed to the local line.

ROSWELL H. HERRICK. 

